When end effectors of robots make physical contact with objects in an environment, including but not limited to objects that are to be acted upon by the robot, the objects may provide environmental impedance due to their mass/weight/stiffness. For example, when a robot positions and operates a gripper-style end effector to grasp and pull an object, the object's weight may provide impedance to the pulling force being applied by the robot. Various aspects of the robot, such as a position of the end effector (sometimes referred to herein as “grasp position”) and a grasp torque applied by the end effector, may be independently adjustable to control how the robot interacts with the object. Grasp torque applied by the end effector may be selectable. Actual grasp force experienced by the end effector may be caused by a combination of the grasp force applied by the end effector, any simultaneous repositioning of the end effector, and the mass/weight/stiffness of the object being interacted with.
End effector constraints of actuators and/or joints of the robot and the amount of impedance applied by the object being interacted with by the robot may impose limits as to how the robot can be safely operated. For instance, these limits may be a set of potential positions of the end effector and corresponding potential grasp torque values that can be safely achieved by the end effector at each potential position. Applying too much grasp torque at a given position, or attempting to reposition the end effector too much when the end effector is experiencing a particular grasp force, may lead to adverse outcomes, such as the end effector missing its precise target (e.g., due to static friction, or “stiction”), undesirable oscillation and/or “hunting,” motor overheating, and in some instances, robot stalling. For example, suppose a gripper end effector is moved to a given position near an outer limit of the robot's reach and grabs an object to be acted upon by the robot. One or more joints or actuators of the robot may consequently be strained to near their operational limits. If a difference (i.e. a grasp force error) between a desired grasp torque value and a potential grasp torque value associated with the given grasp position of the end effector is too great, the robot may cause one or more of these joints or actuators to overheat while attempting to achieve the desired grasp force.